Portable video and film camera lights are generally common. Typically, these lights use a halogen cycle incandescent lamp in an efficient parabolic or elliptical reflector, and are powered by a belt mounted rechargeable battery pack. Early versions of portable lamps used quartz iodine lamps in the 100 W to 150 W power range and ran at a nominal color temperature of 3200.degree. K. Power packs employing rechargeable secondary batteries such as lead-acid, sealed lead calcium or even nickel cadmium cells become unmanageably heavy and awkward if they are designed power 100 Watt lamps for any reasonable length of time. The relatively high levels of illumination developed by these high powered lamps was dictated primarily by the motion picture cameras and color film which were available at the time. Modern video cameras utilizing charge coupled devices or MOS sensors have excellent low light sensitivity and can produce acceptable images at light levels below 10 lux. The requirement for high power video lighting is therefore disappearing and instead only modest auxiliary lighting is needed for most indoor video taping. Furthermore, in most home video situations, distances of only several meters are involved so that lower power lamps are usually adequate. Experience has indicated that 25 Watt high brightness halogen lamps produce enough light for many "close in" taping situations, and are only inadequate at relatively great distances or at very close range, where they can wash out the image highlights due excessive brightness. High brightness video lamps running at high temperature generally last very few hours.
The range of illumination encountered in indoor close up taping and outdoor fill situations is very great. In many applications of auxiliary lighting the dynamic lighting control range of the typical video camera is inadequate. Even though camera lens iris control and image sensor gain can be adjusted, often it is more expedient to control the illumination level by adjustment of the off camera lighting equipment.
There are light responsive devices for controlling various types of lamps, but none are portable and to be used with cameras. One light responsive device is utilized with a control panel, such as on a vehicle. The panel control includes an ambient light sensor, wherein constant contrast illumination control is achieved by pulse width modulation. As the sensor sensing greater ambient light, the pulse widths increase to provide greater illumination. Such a device is disclosed in U.S. Pat. No. 4,368,406 issued Jan. 11, 1983 in the name of Kruzich et al.
A second type of light responsive control is disclosed in U.S. Pat. No. 4,464,606 issued Aug. 7, 1984 in the name of Kane and U.S. Pat. No. 4,682,084 issued July 21, 1987 in the name of Kuhnel et al. Both systems are self-adjusting ballasts for fluorescent lamps. A light sensor maintains the lamps at a predetermined brightness level.
None of the prior art systems disclose a battery powered, portable light for use with cameras which automatically varies lamp output. None of these prior art devices could be used as a portable video lamp.